Technical Abstract:
Chicks are most susceptible to Salmonella infection during the first four days post-hatch. In poultry, one of the primary cells in the innate immune response to early bacterial invasion by Salmonella is the heterophil. Previous studies using a granulocytopenic chicken model in more mature birds demonstrated the significant role heterophils have in the defense mechanism against Salmonella. Studies in the past have also shown the efficiency of heterophils from 3- to 5-week-old chickens to phagocytose and kill Salmonella as compared to the abilities of the monocyte. For the present study, we investigated the phagocytic and bactericidal activities of heterophils from chickens during the first 7 days post-hatch to evaluate whether decreased heterophil function plays a role in the susceptibility of young chicks to Salmonella infections. The phagocytic index of the heterophil did not change between Day 1 and Day 4, but then doubled by Day 7 ( Day 1, 30.69; Day 4, 33.99; Day 7,60.46). Interestingly, the bactericidal activity of the heterophils from all three age groups exceeded 90%. Based on this data, we conclude a relationship exists between the age of the chick, the functional activity of the heterophil, and the susceptibility to organ invasion by Salmonella.